1. Field of the Invention
The present invention relates to a method of measuring distortion of a projection optical system, a method of manufacturing a semiconductor device while correcting distortion, and so forth. In particular, it relates to a distortion measuring method in which a reference wafer is used for measuring deviation of each point from its designed value, a method of manufacturing a semiconductor device while correcting distortion, and so forth.
2. Related Background Art
Conventionally used for measuring distortion of a projection lens in a projection exposure apparatus is so-called reference wafer method in which a reference wafer is employed for measurement. In this method, deviations of individual points on the reference wafer from their respective designed values are determined, point by point, on the basis of coordinates of a coordinate measurement system.